Equipment used in the processing of plastic, such as molds and extrusion screws, is cleaned of plastic residue by a combination of thermal cycling and agitation without impact cleaning. A chamber can be heated by an electric radiant heater and cooled by the introduction of liquid nitrogen. A fixture in the chamber receives the equipment to be cleaned and is agitated by a drive motor. The chamber is heated and cooled in the following cycle in which the drive motor agitates the fixture: first to 250-300° F., then to −315° F., then cycled between −50° F. and −10° F., then to 150° F., then to −200° F., to 100° F., then to ambient temperature. The chamber is controlled by a computer that prompts the operator for the kind of plastic to be cleaned off of the equipment and then controls the heating and cooling automatically.